EFFECTS OF PHASE ABERRATION ON TISSUE HEAT-GENERATION AND TEMPERATUREELEVATION USING THERAPEUTIC ULTRASOUND

The effects of inhomogeneous propagation media on tissue heating patte rns and steady-state temperature distributions are investigated analyt ically for continuous-wave therapeutic ultrasound using a random-phase screen model, Formulas for the statistical moments of the on-axis hea t distribution, total heat deposited in a target volume, and axial tem perature elevation are derived, Based on the statistical moments, we p ropose figures of merit to quantitatively assess therapeutic performan ce for a range of experimental parameters, The analysis relates statis tical properties of the aberrator to those of heat generation in tissu e, The mean on-axis heat distribution is substantially reduced in the focal zone, while its variance is increased at other axial positions, The amount of heat delivered to a target volume depends on the locatio n of the target and the size of the volume, Compared to the results fo r homogeneous media, the greatest reduction in temperature increase oc curs in the focal zone, Distortions in the temperature elevation patte rns are greatest when the perfusion in tissue is large.